Computational Model for Free Abrasive Machining of Brittle Silicon Using a Wiresaw

Abstract

The present paper deals with physics based computational modeling of the wiresaw Free Abrasive Machining (FAM). The wiresaw is used to slice large diameter wafers of predominantly brittle semi-conductors such as silicon. The wiresawing model proposed in the present paper involves cutting action by ‘floating’ abrasives. It is proposed that the abrasive carrying slurry forms a film in the cutting zone by an elasto-hydrodynamic action. Finite Element Analysis shows this film to be in general thicker than the average abrasive size. This signifies a ‘float’ machining condition, wherein there is no direct pressing of abrasives by the wire. Typical rolling and indenting of abrasives under such free body abrasion environment is supported by hydrodynamic shear and pressure respectively. The abrasive is assumed to remove material by typical indentation fracture. Finite element analysis of stresses underneath an indenting abrasive shows that cracks leading to chipping occur only during unloading of indented abrasives (during rolling). The volume of the chip removed in a single indentation is proportional to the volume of plastic zone underneath the indenter. We integrate the elasto-hydrodynamic model and the single abrasive indentation model into a complete representative model of wiresawing.